JP2006030386A - Magnet roll - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnet roll which has magnetic poles prevented from positional deviation even if high rotational torque acts upon a permanent magnet. <P>SOLUTION: The magnet roll has a permanent magnet 2 having a C-shaped section, which has a plurality of magnetic poles including a main magnetic pole (N2), a pair of magnetic poles (S3 and S1) having opposite polarities and has a cut groove between the pair of magnetic poles (S1 and S3), and a shaft 3 stuck to an inner peripheral surface of the permanent magnet 2, and minute gaps 5a and 5b having wedge-shaped sections are formed in an edge part of the inner peripheral surface side of the permanent magnet 2 and are filled with adhesive to form adhesive reservoirs 6a and 6b. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a magnet roll incorporated in an electrophotographic apparatus and used for developing an electrostatic charge image.

  In an electrophotographic apparatus, in order to develop an electrostatic charge image formed on the surface of a photoreceptor, a plurality of magnetic poles arranged asymmetrically on the surface inside a cylindrical body (hereinafter referred to as a sleeve) made of a non-magnetic material. A developing roll provided with a magnet roll having the above is used. The developing roll is disposed such that the main magnetic pole (developing magnetic pole) of the magnetic poles faces the closest position (developing gap) between the photosensitive member and the sleeve, and a magnetic developer (one-component magnetic toner) is placed on the sleeve. Or a two-component developer composed of toner and magnetic carrier) and rotating the sleeve in a predetermined direction, and by rubbing the surface of the photoreceptor with a magnetic brush formed on the developing magnetic pole, The image is developed. After passing through the development gap, the magnetic developer is scraped off from the sleeve, mixed with a new developer, and then used again for development. Therefore, a pair of detaching magnetic poles having opposite polarities to the developing magnetic pole as viewed from the rotation direction of the sleeve are provided.

  As the magnet roll, for example, a plurality of magnet pieces are bonded around the shaft, and the peak magnetic force between the pair of desorption magnetic poles (between the recovery pole and the pumping pole) is set to 100 gauss or less. A structure in which a kerf (gap) is provided between the magnetic poles has been proposed (see, for example, Patent Document 1). However, according to the bonded type magnet roll, it is difficult to make the center of each magnet piece coincide with the center of the shaft, which increases the number of assembly steps. Therefore, a structure in which a cylindrical shaft is inserted and fixed to a permanent magnet having a C-shaped cross section in which a groove (notch) is formed between desorption magnetic poles has been proposed (see, for example, Patent Document 2).

  The structure of the magnet roll 1 described in Patent Document 2 will be described with reference to FIG. This magnet roll is assembled by expanding the kerf 4 and releasing the expansion after inserting the shaft 3 coated with the adhesive on the inner peripheral surface of the permanent magnet 2, so that the number of assembling steps can be reduced. There is. Further, by forming adhesive reservoirs (filled adhesive) 7a and 7b so as to protrude into the cut groove 4 at the inner peripheral edge portion of the permanent magnet 2, the adhesive strength between the permanent magnet and the shaft is improved. Yes. One end 31 of the shaft 3 is reduced in diameter, and a milling surface 32 for positioning the main pole (developing magnetic pole) N2 is formed there.

JP 2001-185415 A (page 3, FIG. 4) Japanese Unexamined Patent Publication No. 2003-1000051 (5th page, FIG. 3)

  In the electrophotographic apparatus, if the developing magnetic pole is deviated from a predetermined position (for example, the closest position between the photosensitive member and the sleeve), the image quality is deteriorated. Therefore, the center of the developing magnetic pole (N2) is usually the milling surface. In addition to being magnetized so as to be at a right angle with respect to 32, it is fixed at a predetermined position of the developing device (with an angle deviation within ± 3 °) with reference to this milling surface 32. Therefore, in an electrophotographic apparatus, in order to obtain a high-quality image even when a large number of sheets (for example, 100,000 sheets or more) are continuously printed, in a magnet roll using a permanent magnet having a C-shaped cross section, Because the contact area between the magnet and the shaft is smaller than that using a cylindrical magnet, even if a circumferential torque is applied to the permanent magnet before the magnet roll is installed in the sleeve, the magnet slips between the permanent magnet and the shaft. It may be confirmed that does not occur. For example, in order to obtain a high-quality image even if continuous printing of 100,000 sheets or more is performed, even if a rotational torque of 294 N · cm (30 kgf · cm) or more is applied to the shaft with a permanent magnet fixed, it is permanent. The standard that no slip occurs between the magnet and the shaft is set. However, in the magnet roll described in Patent Document 2, when rotational torque is applied to the shaft, no slip occurs between the permanent magnet and the shaft until the rotational torque is about 196 N · m (20 kgf · cm). When the torque exceeds 294 N · cm (30 kgf · cm), slipping occurs between the permanent magnet and the shaft, and the angle between the developing magnetic pole and the milling surface serving as the reference surface changes from 90 °. is there.

  Accordingly, an object of the present invention is to provide a magnet roll that does not slide between a permanent magnet and a shaft when a rotational torque is applied to the shaft.

  In order to achieve the above object, a magnet roll of the present invention has a C-shaped cross section having a plurality of magnetic poles including a main magnetic pole and a pair of magnetic poles having opposite polarities, and having a kerf between the pair of magnetic poles. It has a permanent magnet and a shaft fixed to the inner peripheral surface of the permanent magnet, a minute gap having a wedge-shaped cross section is formed at the inner peripheral side edge of the permanent magnet, and the minute gap is filled with an adhesive Thus, an adhesive reservoir is formed.

  In the magnet roll of the present invention, it is preferable that the minute gap has a shape in which the ratio (S / B) of the circumferential length (S) to the radial width (B) is in the range of 5-15. More preferably, the circumferential length (S) is in the range of 0.4 to 1.5 mm and the radial width (B) is in the range of 0.07 to 0.2 mm.

  According to the present invention, a fine gap having a wedge-shaped cross section is formed at the edge portion on the inner peripheral side of the permanent magnet, and the adhesive is filled therewith to form a healthy adhesive reservoir free of bubbles and nests. The permanent magnet is firmly fixed to the shaft, and slipping between the permanent magnet and the shaft is prevented when rotational torque is applied to the shaft. Therefore, with this magnet roll, a high-quality image can be obtained even when many sheets are continuously printed.

Details of the present invention will be described below with reference to the accompanying drawings.
FIG. 1 is a side view of the magnet roll of the present invention. As shown in FIG. 1, a magnet roll 1 includes a permanent magnet 2 having a C-shaped cross section, in which a part of a hollow cylindrical body is cut out, and a cylindrical shaft 3 fixed to an inner peripheral surface thereof. Yes. The shaft 3 has a shape in which one end 31 is reduced in diameter, and a milling surface 32 is formed there. The permanent magnet 2 has a plurality (5 in FIG. 1) of magnetic poles extending in the axial direction on the surface. These magnetic poles are arranged along the rotation direction (counterclockwise) of the sleeve (not shown), the developing magnetic pole (N2), the scraping magnetic pole (S3, S1), the transporting magnetic pole (N1), and the ear-cutting magnetic pole (S2). It is composed of These magnetic poles are magnetized so that the angle formed by the straight line L connecting the center of the developing magnetic pole (N2) and the center C of the shaft 3 and the milling surface 32 is a right angle. In the permanent magnet 2, a kerf 4 is formed between the desorption magnetic poles (S3, S1), and a minute gap 5a having a wedge-shaped cross section is formed at the inner peripheral edge of the permanent magnet 2 facing the kerf 4. 5b is formed and filled with an adhesive to form adhesive reservoirs 6a and 6b.

  FIG. 2 is an enlarged view of a part (part A) of FIG. As shown in FIG. 2, the minute gaps 5a and 5b have a wedge-shaped cross-sectional shape so that the adhesive can be easily filled. With this cross-sectional shape, when the adhesive is cured, the generation of bubbles and nests is suppressed, and the adhesive strength can be increased. Further, with this cross-sectional shape, since the inner peripheral surface of the permanent magnet and the outer peripheral surface of the shaft are opposed to each other at the inner peripheral edge of the permanent magnet, a large adhesive force is easily obtained. When the minute gaps 5a and 5b are formed with other shapes, for example, minute gaps (dents) having a rectangular or fan-shaped cross-sectional shape and filled with an adhesive, a nest is likely to be generated in the depths of the depressions. If the width of the dent is made extremely narrow, in addition to the generation of nests, bubbles are likely to remain. If air bubbles or nests exist in the adhesive reservoir, when torque is applied to the shaft 3, slip occurs between the permanent magnet 2 and the shaft 3 with a torque of less than 294 N · cm (ie, 30 kgf · cm).

The minute gaps 5a and 5b preferably have a cross-sectional shape in which the ratio (S / B) of the circumferential length (S) to the radial width (B) is in the range of 5-15. This is because if the S / B is too small, the adhesive does not penetrate from the edge portion of the permanent magnet 2 to the back, so that a nest is likely to be formed, whereas if the S / B is too large, the adhesive reservoir is easily peeled off. Because it becomes.
In order to further increase the adhesive strength, the circumferential length S is in the range of 0.4 to 1.5 mm, and the radial width B is in the range of 0.02 to 0.7 mm. It is more preferable.

  In the example of FIG. 1, the kerfs 4 are formed in a fan shape, and the magnet end faces are opposed in a non-parallel state across the kerfs 4, but the magnet end faces face each other in parallel from the middle of the kerfs 4. It is good also as a shape to do. According to such a shape, when producing a magnet roll having a small diameter (magnet outer diameter of 20 mm or less), the volume of the kerf 4 is reduced, but still, the adhesive is quickly filled into the minute gap. be able to.

  Said magnet roll 1 can be assembled in the following procedure, for example. First, the permanent magnet 2 is prepared. The permanent magnet 2 can be formed of, for example, a sintered ferrite magnet or a resin magnet. When using a resin magnet, for example, prepare a compound mainly composed of magnet powder and thermoplastic resin (binder), heat knead, and then extrusion molding (in the case of extrusion molding, cut into a predetermined length after molding) Or may be molded integrally by injection molding. When performing the above extrusion molding or injection molding, the isotropic magnet may be formed in a non-magnetic field by a required magnetic flux density, but may be an anisotropic magnet by applying an orientation magnetic field to the molding space. . Examples of the magnet powder include ferrite magnetic powder such as barium ferrite and / or strontium ferrite, strontium ferrite magnetic powder containing La and Co, or R-Co, R-Fe-B, and R-Fe-N. Rare earth magnetic powder can be used, or a mixed powder of the ferrite magnetic powder and the rare earth magnetic powder can be used, but in terms of cost, ferrite magnetic powder such as barium ferrite and / or strontium ferrite is used. It is advantageous. Examples of the thermoplastic resin include thermoplastic resins such as polyethylene, vinyl chloride, ethylene-ethyl acrylate copolymer (EEA), ethylene-vinyl acetate copolymer (EVA), polyacetal, and ABS resin. In addition, an appropriate amount of a lubricant, a plasticizer and the like can be added to the compound.

  When extrusion molding or injection molding of the permanent magnet 2 is performed, a protrusion having a shape corresponding to a minute gap having a wedge-shaped cross section may be provided on the mold (core metal). Moreover, what is necessary is just to process after sintering, when using a sintered magnet. After the adhesive is applied to the inner peripheral surface of the permanent magnet 2 or the outer peripheral surface of the shaft 3 manufactured as described above, the shaft 3 is fixed to the inner peripheral surface of the permanent magnet 2, and then, for example, the micro gaps 4a and 4b By filling the instantaneous adhesive and forming the adhesive reservoirs 5a and 5b, the permanent magnet 2 and the shaft 3 can be firmly fixed. In particular, by reducing the gap size to some extent, it becomes possible to withstand rotational torque exceeding 588 N · cm (ie, 60 kgf · cm). When this magnet roll is used, even if continuous printing exceeding hundreds of thousands of sheets is performed, the developing magnetic pole is held at a predetermined position, and a high-quality image can be obtained.

  FIG. 3 is a side view of a magnet roll according to another embodiment of the present invention. As shown in FIG. 3, the magnet roll 1 is provided with a concave groove in a portion where the developing magnetic pole (N2) of the permanent magnet 2 is formed, and there is a permanent magnet having higher magnetic characteristics than the permanent magnet 2, for example, anisotropic 1 except that a block magnet 21 made of a rare earth resin such as an SmFeN bonded magnet is embedded and an arc-shaped (for example, semicircular) positioning groove 22 is formed at the center of the end surface (S3 pole side) of the permanent magnet 2. It has the following structure. By providing the positioning groove 22 on one end face of the permanent magnet 2, it can be visually determined that the S3 pole is present, so that an assembly error can be prevented. The semicircular positioning groove 22 can be easily formed by providing a semicircular protrusion on the magnet molding die.

  According to the magnet roll shown in FIG. 1, development is performed as shown in FIG. 4, for example. A developing roll 10 in which the magnet roll 1 is incorporated in the sleeve 11 is disposed around the photoreceptor 100. The development gap Dg formed at the position where the surface of the photoreceptor 100 and the sleeve 11 are closest to each other is adjusted to a predetermined value, and the doctor gap d formed between the tip of the doctor blade 12 and the sleeve 11 is also adjusted. It is adjusted to a predetermined value (for example, a value equivalent to Dg). Further, the magnet roll 1 is fixed so that the developing magnetic pole (N2) faces the developing gap Dg, and the spiked magnetic pole (S2) faces the tip of the doctor blade 12. In this state, when the photosensitive member 100 is rotated clockwise (arrow X direction) and the sleeve 11 is rotated counterclockwise (arrow Y direction), a magnetic developer (not shown) held on the surface of the sleeve 11 is obtained. Is conveyed in the same direction as the sleeve 11, passes through the doctor gap d, contacts the surface of the photoconductor 100 at and around the development gap Dg, and an electrostatic charge image (not shown) formed on the surface is developed. The The magnetic developer after passing through the development gap Dg is scraped off from the surface of the sleeve 11 by the repulsive magnetic field of both when passing through the desorption magnetic poles S3 and S1, and is collected in the developer tank (not shown). Then, after being mixed with a new developer, it is adsorbed by the conveying magnetic pole (N1), and the above developing process is repeated again.

  The magnet roll shown in FIG. 1 was produced by the following procedure. First, a mixed medium (polyvinyl alcohol) is added to 12 parts by mass of EEA and 88 parts by mass of Sr ferrite, heated and kneaded, and this kneaded material is put into an extruder, so that a compact with a C-shaped cross section is formed in a magnetic field. Extruded. The molded body extruded from the outlet of the mold is cut into a predetermined length, and after drying, 5-pole asymmetric magnetization is applied, so that the outer diameter is 23 mm, the inner diameter is 8 mm, and the axial length is 304 mm. A permanent magnet 2 having a minute gap 5a, 5b having a wedge-shaped cross section in the part was produced. Inserted into this permanent magnet 2 is a SUS304 shaft 3 having an outer diameter of 8 mm and coated with an anaerobic adhesive mainly composed of a polyester-type acrylic diester on the outer peripheral surface, and is cured at room temperature. After the shaft 3 was fixed, the minute gaps 5a and 5b were filled with a cyanoacrylate instantaneous adhesive and cured at room temperature to form adhesive reservoirs 6a and 6b. Here, nine types of magnet rolls were produced by changing the dimensions of the minute gaps 5a and 5b. Table 1 shows the dimensions of the minute gaps 5a and 5b formed in these magnet rolls. For comparison, four types of micro gaps 5a and 5b having different dimensions are the same as described above except that the shape of the micro gaps 5a and 5b is rectangular (the width B is uniform along the outer peripheral surface of the shaft). A magnet magnet roll was prepared.

Each of the above magnet rolls was placed in an aluminum alloy sleeve, and the magnetic flux density in the normal direction of the sleeve was measured on the sleeve surface. The maximum magnetic flux density of the developing magnetic pole (N2) was 110 mT and the half-value angle was 45 degrees. Among the other magnetic poles, the maximum magnetic flux density of the magnetic pole having the largest magnetic force was 90 mT. The intervals between the magnetic poles were θ ₁ = 75 °, θ ₂ = 60 °, θ ₃ = 90 °, θ ₄ = 65 °, and θ ₅ = 70 °.

  For each magnet roll 1, with the permanent magnet 2 supported by the fixed portion, a rotational torque is applied to the shaft 3, and the angle formed between the center of the developing magnetic pole and the milling surface is measured. The presence or absence of slippage (magnetic pole position deviation) between the two was confirmed. Table 1 shows the relationship between the value of the rotational torque applied to the shaft 3 and the positional deviation of the magnetic poles.

  From Table 1, when the shape of the minute gap is wedge-shaped, the gap width (B) is 0.07 to 0.20 mm and the gap length (S) is 0.7 mm or 1.2 mm (experiment). 1 and 2) Even when a rotational torque of about 600 N · cm (80 kgf · cm) or more is applied to the shaft (corresponding to hundreds of thousands of continuous printing), it can be seen that the magnetic pole is not misaligned. However, even when the shape of the minute gap is wedge-shaped, if the gap width (B) is 6.0 mm or 8.0 mm and the gap length (S) is 0.4 mm or 0.8 mm (Experiment 3) It can be seen that even when a rotational torque of 245 to 284 N · cm (31 to 36 kgf · cm) is applied to the shaft (corresponding to 100,000 continuous printing), the magnetic pole can be prevented from being displaced.

  On the other hand, in Experiment 4, since the gap is rectangular, it can be seen that when a rotational torque of 196 N · cm (15 kgf · cm) or more is applied to the shaft, the magnetic pole is displaced. Further, in this magnet roll, the permanent magnet was cut in the longitudinal direction and filled into a rectangular gap, and as a result of observing the cross section of the adhesive, the presence of a nest was recognized inside the adhesive.

It is a side view of the magnet roll concerning embodiment of this invention. It is the side view to which the principal part of FIG. 1 was expanded. It is a side view of the magnet roll concerning other embodiment of this invention. It is a figure which shows typically the positional relationship of the developing roll provided with the magnet roll of FIG. 1, and a photoreceptor. It is a side view which shows an example of the conventional magnet roll.

Explanation of symbols

1: magnet roll, 2: permanent magnet, 21: block magnet, 22: positioning groove, 3: shaft, 31: reduced diameter portion, 32: milling surface, 4: notch, 5a, 5b: minute gap, 6a, 6b : Adhesive reservoir, 10: Developing roll, 11: Sleeve, 12: Doctor blade, 100: Photoconductor

Claims (3)

A permanent magnet having a C-shaped cross section having a plurality of magnetic poles including a main magnetic pole and a pair of magnetic poles having opposite polarities and having a groove between the pair of magnetic poles, and fixed to the inner peripheral surface of the permanent magnet A magnet having a shaft, a minute gap having a wedge-shaped cross section is formed at an inner peripheral edge portion of the permanent magnet, and an adhesive reservoir is formed by filling the gap with an adhesive. roll. The minute gap has a shape in which a ratio (S / B) of a circumferential length (S) and a radial width (B) is in a range of 5 to 15. Magnet roll. The circumferential length (S) is in the range of 0.4 to 1.5 mm, and the radial width (B) is in the range of 0.07 to 0.2 mm. Item 3. A magnet roll according to item 2.

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